Distribution of the density of states of bonded hydrogen in amorphous hydrogenated silicon

Hydrogen-induced metastability is analysed by a density of states distribution for bonded hydrogen, which described the alternative hydrogen sites and the effects of disorder. The metastability is explained by the redistribution of hydrogen following illumination, annealing or a shift of the Fermi energy. Hydrogen and defect equilibria are related to the hydrogen diffusion and the chemical potential. An estimate of the hydrogen density of states distribution, based on the weak bond model, is shown to be consistent with the measured defect density. Irreversible metastable changes are related to structural reconstructions which change the shape of the distribution, while the reversible changes correspond to a redistribution of hydrogen within an approximately constant density of states.